An image sensor is a semiconductor device for converting an optical image into an electric signal, which is generally classified as a charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS) image sensor.
The CCD has several disadvantages such as a complicated driving mode, a high power consumption and a complicated fabricating process due to the number of multi-step photo processes. Also, the CCD has another disadvantage in that it is difficult to integrate a control circuit, a signal processing circuit and an analog-to-digital (A/D) converter circuit into a single chip.
Therefore, in recent years, the CMOS image sensor has received attention as a next-generation image sensor to overcome the shortcomings of the CCD.
The CMOS image sensor is a device employing a switching mode that sequentially detects outputs of each unit pixel using MOS transistors using a control circuit and a signal processing circuit as peripheral circuits. The MOS transistors are formed using a CMOS technology in each unit pixel. The CMOS image sensor has advantageous merits such as low power consumption and simplified fabrication process due to the relatively small number of photo processing steps. In addition, since it is possible to integrate a control circuit, a signal processing circuit and an A/D converter circuit, into a CMOS chip, the CMOS image sensor is easy to use in compact products.
FIG. 1 is a cross sectional view of an image sensor according to a related art.
Referring to FIG. 1, an image sensor includes a metal pad 4 formed on a semiconductor substrate 2, a metal pad opening 6 exposing the metal pad 4, a first planarization layer 8, a color filter array 10, a second planarization layer 12 and a microlens 14.
The color filter array 10 for realizing a color image may consist of three colors such as red, green and blue or yellow, magenta and cyan.
However, in a manufacturing process of an image sensor according to the related art, because a photosensitive layer used for forming each color filter is removed by etching for a predetermined time, the photosensitive layer is not always completely removed from the metal pad opening, which causes the metal pad to be contaminated with the remaining photosensitive layer.
The photosensitive layer is also not completely removed but remains on the respective color filters so that cross sections of the color filters may not be planarized. As a result, a gap may occur between color filters, causing an undesirable light beam to flow into a photodiode.